Sourdough Starter:

1. Feed your sourdough starter, ensuring you have about 1 cup of active starter. Reserve leftovers for future use.

Mixing the Dough:

1. In a bowl, combine warm water, honey, malt syrup, and barley malt powder. Let it sit for 10 minutes to activate the yeast.
2. In the bowl of your stand mixer, mix white bread flour, rye flour, and kosher salt. Add eggs and the yeast mixture. Mix on low speed until just combined.
3. Increase the mixer speed to medium and knead for about 10 minutes until you have a smooth dough.
4. Slowly add the butter at room temperature, 1 tbsp at a time, kneading for another 10 minutes until the dough is smooth and elastic.

Choose one of two options:

1. Leave the dough covered outside the fridge for about 3 hours or until doubled in size for same-day baking.
2. Cover the dough and refrigerate overnight for improved flavour through slow sourdough fermentation.

Forming the Buns:

1. Take the dough, form it into a round shape, and divide it into 8 large or 10 medium buns.
2. Tuck the edges under and shape into round buns. Place them on parchment-lined baking trays, cover with clingfilm or damp tea towels, and let them rest outside the fridge for an additional hour.

Boiling:

1. Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper.
2. In a large pot, bring 2 litres (4.2 pints) of water to a boil. Carefully add baking soda bit by bit, stirring until it dissolves.
3. Gently drop the pretzel buns into the boiling water, allowing them to boil for about 30 seconds on each side. Use a slotted spoon to transfer them to the prepared baking sheet.
4. Sprinkle the buns with flaky sea salt and sesame seeds if desired. Use a sharp knife to slice them crosswise.

Baking:

1. Bake the pretzel buns in the preheated oven for 15-20 minutes or until they turn golden brown on top.
2. Serve with your favourite toppings, for dipping, as a side to stew, or on their own with cold butter.
3. Enjoy your delicious homemade Sourdough Brioche Pretzel Buns!